At present, Light Emitting Diode (LED) display panels are mainly encapsulated by using frit. FIG. 1 is a schematic cross-sectional view of an existing LED display panel, in which a first substrate 1 and a second substrate 2 are encapsulated together by a sealant 3 (e.g., frit) interposed therebetween, and a light emitting unit 4 is disposed on the second substrate 2. In the encapsulation process, a laser is used to irradiate the solid sealant 3 to melt it. After the sealant 3 is solidified again, the first substrate 1 and the second substrate 2 can be encapsulated together.
The laser can only irradiate a part of the sealant 3 at a time. When the part of the sealant 3 is melted, stress release phenomenon may happen between the first substrate 1 and the second substrate 2. The released stress tends to separate the two substrates, such that the sealant 3 fails to effectively encapsulate the first substrate 1 and the second substrate 2. Thereby, the problem of poor encapsulation occurs.
With respect to the above problem, one solution in prior art is to dispose a thermally-expansible layer and other interlayers on the outer side of the first substrate 1 (i.e., the side away from the second substrate 2). When the sealant 3 is irradiated by the laser and then melted, the generated heat is transferred to the thermally-expansible layer at the same time. The thermally-expansible layer is heated and then expands, thereby pressing the first substrate 1 against the second substrate 2 to prevent the two substrates from being separated due to the released stress. However, this solution requires the laser to be kept irradiating from the bottom up (i.e., irradiating from the second substrate 2 towards the first substrate 1), and thus is inconvenient for operation. Besides, because the thermally-expansible layer is generally made from organic macromolecule material or elastic rubber material, it tends to cause environmental pollution.
Another solution in prior art is to add a pressure plate assembly on each of the outer sides of the first substrate 1 and the second substrate 2, so as to provide clamping force for the first substrate 1 and the second substrate 2. Besides, a sensor is disposed to sense the magnitude of the pressure between the pressure plate assemblies, such that poor sealing effect due to unduly small clamping force or device damage due to unduly large clamping force can be avoided, thereby improving the encapsulation quality. However, when this solution is used for encapsulation, because the interval between the first substrate 1 and the second substrate 2 is very small (generally below 20 μm), it is difficult for the sensor to effectively sense the magnitude of the pressure between the pressure plate assemblies. Furthermore, it is also difficult to effectively integrate the sensor with the two substrates.